1. Field of the Invention
This disclosure relates to a flame retardant electrolyte solution for a rechargeable lithium battery, and a rechargeable lithium battery including the same.
2. Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as a power source for small portable electronic devices. They use an organic electrolyte solution and thereby have twice the discharge voltage of a conventional battery using an alkali aqueous solution, and accordingly have high energy density.
For positive active materials of a rechargeable lithium battery, lithium-transition element composite oxides being capable of intercalating lithium such as LiCoO2, LiMn2O4, LiNi1−xCoxO2 (0<x<1), and the like have been researched.
As for negative active materials of a rechargeable lithium battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon, which can all intercalate and deintercalate lithium ions, have been used.
As for an electrolyte solution, a lithium salt dissolved in a carbonate-based solvent has been generally used. Recently, in order to improve flame retardancy of an electrolyte solution, a mixture of cyclic and linear carbonate solvents including a phosphoric acid-based retardant in an additive amount has been suggested.
However, the phosphoric acid-based retardant causes reductive decomposition in a reaction between a negative electrode and the electrolyte solution to decrease available capacity of the negative electrode and increase cell resistance. Thereby, it suppresses a smooth intercalation reaction of lithium ions.
Furthermore, if the phosphoric acid-based retardant is added in an excessive amount in the form of a solvent instead of in an additive level, the cycle-life characteristics of a battery produced therewith are significantly decreased.